Thermocouple containing devices have long been used to measure temperatures within reactors or chambers, such as may be used in the chemical and refining industries. Examples of such uses are described in U.S. Pat. Nos. 3,015,234; 3,263,502; 3,637,438; 3,864,975; 3,901,080; 4,376,227; and 4,625,200. Many examples of the prior art permit such measurement at a number of discrete levels of the reactor. At least two of the mentioned patents (see U.S. Pat. Nos. '502 and '227) describe, as a means for performing such plural measurements, the insertion of a flexible support, having a plurality of thermocouple cables wrapped therearound, into a well which well is positioned within the reactor. Although such arrangements represented vast improvements over the then prior art, at least one unfortunate problem was not fully solved Accumulations of harmful materials, such as corrosive vapors or liquids, formed within the well. These materials can cause deterioration of the well, materials in which the thermocouple elements may be encased, and can cause failure of the temperature measuring members, i.e., thermocouples themselves. This invention was intended to minimize the problems associated with the concentration of contaminants within the protective well, without sacrificing the flexibility, accuracy, and response characteristics of the temperature measuring system.